The presently existing houses take up as many tiles on the outworld map as they have avaliable on the inside. This is realism.
It could be argued that giving the houses more space on the inside than they actually take up on the outside, could be seen as an abstraction of the fact that the space inside a house is more accessible, better disposed, more easily controlled and, frankly, more important, than space outside the house. This is not realism, but perhaps better gameplay. I don't really know which is best.
Question: Should houses have larger areas available indoors than they actually take up space in the main world?